A better way to call Class Methods from List of Class Objects - Python

Question

I was working on Python Classes and found that one cannot call class method from class object by looping through a list of such objects. Below is a sample code:

def show_student_details(*s_list):
    for s in s_list:
        print("Roll Number: ", s.get_roll_no())
        print("Name: ", s.get_name())
        print("Phone: ", s.get_phone())
        print("Marks: ", s.get_marks())

The code for Student class is:

class Student:

    def __init__(self, roll_no=0, name="", phone="", marks=-1):
        self.__roll_no = roll_no
        self.__name = name
        self.__phone = phone
        self.__marks = marks

    def get_roll_no(self):
        return self.__roll_no

    def get_name(self):
        return self.__name

    def get_phone(self):
        return self.__phone

    def get_marks(self):
        return self.__marks

Running this piece of code by passing some objects of Student class gives the following error:

  File "main.py", line 88, in <module>
    show_student_details(students)
  File "main.py", line 12, in show_student_details
    print("Roll Number: ", s.get_roll_no())
AttributeError: 'list' object has no attribute 'get_roll_no'

The thing I understand is that List is itself a Class and Python interprets this code as if I was calling the get_roll_no() function on List Object.

I googled this problem and found that map() and methodcaller() can be used to call the class methods but they didn't work for me.

I know that this question has been asked multiple times on StackOverflow but I think none of them solved my problem which is 'calling multiple class methods from object by selecting objects one by one from a list of class objects.'

Any help will be appreciated. Thanks in Advance.

Alireza Tajadod · Accepted Answer · 2020-01-29 16:28:28Z

1

Assuming you are passing a list of students to the function such as ([<__main__.Student object at 0x122d85990>, <__main__.Student object at 0x122d85910>],), you can use :

def show_student_details(*s_list):
for s in s_list[0]:
    print("Roll Number: ", s.get_roll_no())
    print("Name: ", s.get_name())
    print("Phone: ", s.get_phone())
    print("Marks: ", s.get_marks())

Because *s_list converts your input to a list. Alternatively, you should be able to just use

def show_student_details(s_list):
for s in s_list:
    print("Roll Number: ", s.get_roll_no())
    print("Name: ", s.get_name())
    print("Phone: ", s.get_phone())
    print("Marks: ", s.get_marks())

answered Jan 29, 2020 at 16:28

Alireza Tajadod

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3 Comments

Rohit Rawat Over a year ago

Thank you @Alireza. Using variable length arguments was causing a problem here. Now I get it.

Tryph Over a year ago

an alternative could be to unpack the list at function call: show_student_details(*s_list). It depends on what the OP really wants

Rohit Rawat Over a year ago

@Tryph that doesn't work for me. But the second code in Alireza's answer works well. Thanks.

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